β-US2 with the orthorhombic structure is an interesting compound of which the electrical property is changed from a metallic state to an insulating state at temperatures lower than 80 K. To clarify the present metal-insulator change, we carried out the magnetization and magnetoresistance measurements in magnetic fields up to 50 T. The magentization at 4.2 K saturates above 40 T, reaching 1.75 μB/U at 50 T for the magnetic field along the magentic easy-axis, namely the  direction. The corresponding electrical resistivity at 4.2 K is steeply reduced in magnitude from 1 × 103 Ω·cm to 2 × 10-2 Ω·cm at 50 T only when the magnetic field is applied along the  direction. The temperature dependence of the electrical resistivity at 50 T indicates a usual metallic behaviour. The conduction electrons are most likely released from the trapped U-sites when the 5f-CEF magnetic moments are fully polarized in high magnetic field of 50 T. The present experimental results are discussed from the viewpoint of the magnetic polaron.
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